Hypoglycemia is an important glucose related complication of diabetes. A common blood glucose monitoring method is an invasive method which periodically measures the blood glucose of a patient by obtaining a blood sample from an individual by a variety of methods, such as by needle or lance. The individual inserts a plastic strip carrying chemistry into a blood glucose meter and then applies a blood sample onto the strip for the measurement of blood glucose concentration by determination of change in reflectance or electric signal of a biosensor. This method produces measurements that, while very accurate, are too infrequent to detect hypoglycemic episodes. Frequently, in order to avoid hypoglycemia, diabetics maintain abnormally high blood glucose levels to prevent low blood glucose levels in between blood glucose measurements. This constant high blood glucose level often causes long-term complications, namely, retinopathy, neuropathy, nephropathy, and cardiovascular disease. In effect, the present blood glucose monitoring methods are forcing many diabetics to pay for a lower rate of acute complications with a higher rate of chronic complications later in life.
Thus, the most important factor for reducing diabetes-associated complications is the maintenance of an appropriate level of blood glucose. The maintenance of the appropriate level of blood glucose may prevent and even reverse many of the effects of diabetes.
Recently, new non-invasive approaches of measuring the level of blood glucose have been pursued. For example, U.S. Pat. No. 4,509,531 discloses a physiological monitor that continuously monitors changes in galvanic skin resistance and/or temperature of the wearer in order to detect the onset of a hypoglycaemic state. Similarly U.S. Pat. No. 4,365,637 discloses a device that senses the buildup of perspiration on the skin of the wearer in order to detect the onset of insulin shock. The main problem with these approaches is that they monitor symptoms of hypoglycaemia or insulin shock and are not necessarily correlated with the level blood glucose. Thus, these approaches are not suited for commercial use as they generate an unacceptable level of false alarms.
U.S. Pat. No. 5,676,143 and U.S. Pat. No. 5,551,422 disclose a method and apparatus for analytical determination of glucose in a biological matrix by measuring the relative intensity of scattered light in a tissue boundary and deriving a blood glucose concentration value. The main problem with this approach is long term drift errors in the estimation of blood glucose values because the initial calibration is not specific to the individual wearing the device and there is no periodic recalibration using an external reference blood glucose meter. Thus it is subject to many interfering parameters that may affect the measurement with time.
U.S. Pat. No. 6,882,940 discloses methods and devices for prediction of hypoglycemic events by obtaining a series of glucose measurement values, performed using a near-IR spectrometer, and skin conductance and/or temperature values. Once again, the main problem with this approach is long term drift errors in the estimation of blood glucose values because the initial calibration is not specific to the individual wearing the device and there is no periodic recalibration using an external reference blood glucose meter. Thus it is subject to many interfering parameters that may affect the measurement with time.
U.S. Pat. No. 6,066,847 discloses a procedure for verifying the accuracy of a non-invasive blood glucose measurement instrument by electrically connecting the instrument to a reference blood glucose meter. In the case there is too much discrepancy between the two measurements, the procedure prevents the individual from continuing to use the non-invasive blood glucose measurement instrument. The problem with such an approach is that once a discrepancy has been detected the non-invasive blood glucose measurement instrument is no longer usable until it is recalibrated.